Methanediol is listed as one of the main ingredients of "Brazilian blowout", a hair-straightening formula marketed in the US.[5] The equilibrium with formaldehyde may cause some concern as formaldehyde in hair straighteners is a health hazard.[6] However the assumption of chemical and toxicological equivalence between formaldehyde (a reactive gas) and methylene glycol (a stable reaction product that forms in an aqueous solution forming the main portion of formalin preparations) is disputed as a conservative assumption (mostly due to the methods of testing that are unable to differentiate the forms) instead of based on empirical toxicological data. According to Golden and Valentini the use of hair products containing less than 3% methelene glycol under controlled conditions should be considered safe from formaldehyde dangers.[7]